1. Field of the Invention
The present invention relates to a recording apparatus, and more particularly to a recording apparatus capable of supplying a recording head with image data at a high speed.
2. Related Background Art
For the purpose of recording on a recording medium such as paper or OHP sheet (hereinafter simply called recording sheet or sheet), there have been proposed recording apparatus with various types of recording heads. Such recording heads are known, for example, as the wire dot type, thermosensitive type, thermal transfer type, ink jet type etc. Among these, the ink jet recording head is attracting attention because of low running cost and low noise, as it is designed to directly discharge ink onto the recording sheet.
Among the ink jet recording apparatuses there is proposed an apparatus designed to discharge ink from discharge openings toward the recording medium, utilizing bubbles generated by thermal energy, thereby recording characters or patterns on said medium.
Such recording apparatus, in which the heat-generating resistor provided in each discharge opening is significantly smaller than the piezoelectric element employed in the conventional ink jet recording apparatus, allows to arrange multiple discharge openings at a high density and has the advantage of providing recorded images of high quality, with a high speed and low noises.
FIG. 1 is a block diagram of the control system for controlling various units of a conventional recording apparatus, in which there are shown an MPU 1 for controlling the entire apparatus through signal exchange with various units thereof; a ROM 2 storing the sequences of control; a RAM 3 used for example as a buffer for the recording data; an interface 4 for information exchange with a host apparatus such as a computer; and an I/O port.
Control signals from the MPU 1 are supplied, through the I/O port 5, to driver circuits 9A, 31A, 35A to control a recording head 9, a carriage motor 31 and a transport motor 35. Also information from a sensor 6 or an operation panel 7 are supplied through the I/O port 5 to the MPU 1.
Now reference is made to a flow chart shown in FIG. 2, for explaining the actual recording operation. After the power supply is turned on in a step S1, there is conducted an initializing operation, such as the detection of home position of a carriage 11 (step S2). If an ON-LINE mode is selected on the operation panel 7 in a step S3, a step S4 enters the recording data, supplied from the host apparatus through the interface 4, into an input buffer area of the RAM 3. Then the MPU 1 converts said data, such as character codes, entered into said input buffer area, into dot matrix image data and stores thus converted data in an image buffer area of the RAM 3. After the image data of a line are prepared in this manner, a step S5 advances the recording sheet by the transport motor 35.
Then the image data to be recorded on the recording sheet are transferred from the image buffer area of the RAM 3 to the I/O port 5 (step S6). Then, a subsequent step S7 effects data analysis for the next line, namely entry of the recording data into the reception buffer area, data conversion into image data and storage of said image data into the image buffer area. Said image buffer area is selected different from that used in the step S6, in order to prevent the loss of the image data. Then, the carriage motor 31 is activated to move the carriage 11 (step S8), and, upon its arrival at the recording position (step S9), a step S10 sends a recording head drive start signal (not shown) to the driver circuit 9A through the I/O port 5. In response the driver circuit 9A drives the recording head 9 according to the image data supplied from the I/O port 5.
The steps S6 to S10 are repeated until the recording of a line is completed, and, upon its completion (step S11), the sequence returns to the step S4.
In such conventional structure, however, the time required by the MPU 1 for the storage of the recording data in the input buffer or the transfer of the image data to the recording head with the increase in the resolving power of the recording head, as the amount of image data to be recorded increases. Thus, within a given drive time of the recording head, the proportion of the image data transfer increases, and accordingly decreases the time allotted to other processes, namely the entry of recording data for the next line into the input buffer area, conversion of said recording data into image data and storage of said image data into the image buffer area.
This drawback becomes particularly conspicuous when the recording head is capable of high-speed recording, such as the aforementioned ink jet recording head utilizing thermal energy. After the completion of recording of a line, the recording operation for the next line is not started until the image data for said next line are prepared, so that there will result a decrease in the recording speed, giving rise to a loss in the throughput.
Also there is required a large memory capacity, because there are provided image buffer areas at least for two lines, in order to prevent the loss of image data as explained above. The increase in the memory capacity is particularly significant when the resolving power of the recording head is high, as in the aforementioned ink jet recording head utilizing thermal energy (hereinafter called bubble ink jet recording head), since the memory capacity required for the image buffer area is proportional to the square of the resolving power of the recording head.
Furthermore, the amount of image data transferred from the host apparatus increases for a recording apparatus capable of high-density recording, such as a bubble ink jet recording apparatus. In such case, unless said recording apparatus is capable of receiving the data at a high speed, the host apparatus is inevitably occupied by the recording apparatus for a long time, so that the throughput of the host apparatus is deteriorated.